292 



The Scottish Naturalist. 



Polygonum Persicaria, P. lapatMfolium, &c; but mingled with them 

 are a host of other and more enduring species, which, if circum- 

 stances are favourable, will help to build up the future vegetation. 

 In young shingles, however, these, like the annual weeds, will 

 probably be swept away by the first flood ; and their successors 

 will not secure a permanent foot-hold till the shingle or stanir has 

 begun decidedly to grow. 



When the shingle has reached that stage at which it is unsub- 

 merged for a considerable part of the year it begins to exhibit a 

 •characteristic flora, the chief feature of which is the presence of 

 Silene maritima, Armeria maritima, Plantago maritima, 

 Alchemilla alpina, Saxifraga aizoides, Oxyria digyna, Viola canina, 

 ■and the naturalised Lupinus perennis. Of these the Silene, the 

 Viola and the Lupinus are. — in Perthshire — almost restricted to the 

 river shingles. Silene maritima does grow in a few places on 

 mountain rocks, but does not occur on the lower or salt-water 

 Perthshire part of the Tay, whilst it may be found on almost every 

 shingle from Perth upwards. On these shingles it is mostly con- 

 fined to the parts where the vegetation is not too dense, for, as 

 other plants increase, it is choked out. 



The Armeria and Plantago are of a more enduring nature ; and 

 continue to maintain their position even when a shingle has 

 become more or less meadow-land, provided that they are not 

 overshadowed by bushes or other tall plants. Whilst abounding 

 in the salt-marshes of the Tay, they (but more especially the 

 Plantago) are of not unfrequent occurrence on the mountains. 

 Viola canina, though not entirely restricted to the shingles, is 

 certainly far more abundant on them than in other spots in 

 Perthshire ; and, curiously enough, the latter places, — peaty 

 moors and dry rocky hills, — are very different in their nature from 

 the shingles. The Lupine, — which now extends over 45 miles of 

 the course of the Tay, and abounds in many places, is most 

 common in the island-shingles or stanirs, many of which are blue 

 with it when it is in flower. Its seeming preference for islands is 

 said to be due to the fact that on the mainland it is eaten by 

 rabbits and thus kept down. 



Of the three alpine species mentioned above the Oxyria sticks 

 to the uncrowded shingles, while Alchemilla alpina and Saxifraga 

 aizoides have spread to the river-side rocks. The Oxyria and 

 Alchemilla have doubtless been brought down from the hills, but 



